The hardest-hit airport as of late Saturday morning was St. Louis, where more than 100 combined arrivals and departures were canceled as more than a foot of snow fell in the area. Airports in Indianapolis and Kansas City, Missouri, were among others seeing above-average cancellations because of the storm.

Most big airlines were waiving change fees for at least some airports in the path of the storm, which was expected to bring additional snow to the Ohio Valley and Mid-Atlantic by Sunday evening. Among the busier airports where flights could be affected into the weekend: Chicago O’Hare, Chicago Midway, Washington Dulles, Washington Reagan National, Indianapolis and Cincinnati.

Another 40 flights had already been grounded for Sunday, mostly preemptive cancellations made by Southwest Airlines at airports like Baltimore/Washington, Chicago Midway and St. Louis, according to FlightAware.

All four of the USA’s biggest airlines were waiving rebooking fees for some airports because of the storm, though the details were different at each of American, Delta, United and Southwest airlines.

Other carriers that had issued storm-related waivers by Saturday morning included JetBlue, Frontier and Spirit.